Gas turbine combustion chamber with modified wall thickness

ABSTRACT

A gas turbine combustion chamber, including at least one combustion chamber wall in which mixed air holes are formed in a predefined area that extends around the combustion chamber in a ring-shaped manner with respect to the central axis of the combustion chamber in a central area of the same, characterized in that the combustion chamber wall has a greater thickness in the ring-shaped area of the mixed air holes than in the areas that are not provided with mixed air holes.

This application claims priority to German Patent Application DE102014226707.2 filed Dec. 19, 2014, the entirety of which is incorporated by reference herein.

The invention relates to a gas turbine combustion chamber according to the generic term of claim 1.

In particular, the invention relates to a gas turbine combustion chamber with at least one combustion chamber wall, inside of which mixed air holes are formed in predefined areas.

It is known from the state of the art to provide mixed air holes in combustion chamber walls of gas turbines, through which additional air is guided into the interior of the combustion chamber.

As far as the state of the art is concerned, reference is made to EP 1 528 322 A2, EP 1 795 809 A2 or U.S. 2002/0116929 A1.

Through the mixed air holes, a considerable weakening is introduced into the combustion chamber wall at a particular axial position. As the share of mixed air is increased through a better cooling and/or through enhanced, more solid wall materials, it is possible to configure the mixed air holes to be bigger. As a result, the strength of the combustion chamber wall is increasingly weakened. This weakening occurs due to the fact that single-layer or double-layer combustion chamber walls are manufactured from sheet metals or cast parts with a constant wall thickness. Cracks occur as a consequence of this material weakening. Here, the crack growth from mixed air hole to mixed air hole is a significant factor when it comes to the failure of combustion chamber walls. Thus, the danger of failure increases with an increasing share of mixed air.

The invention is based on the objective of creating a gas turbine combustion chamber of the kind that has been mentioned in the beginning, in which the disadvantages of the state of the art are avoided and which in particular has a sufficient strength in the area of the mixed air holes, while at the same time having a simple structure and being manufacturable in a cost-effective manner.

According to the invention, the objective is achieved by the combination of features of claim 1, with the subclaims showing further advantageous embodiments of the invention.

Thus, it is provided according to the invention that the combustion chamber has a greater wall thickness in the area of the mixed air holes than in the areas that are not provided with mixed air holes.

The mixed air holes are arranged in a middle area of the combustion chamber with respect to the axial extension of the combustion chamber, and in the circumferential direction of the combustion chamber. According to the invention, this ring-shaped circumferential area in which the mixed air holes are arranged is provided with a greater wall thickness.

Thus, according to the invention, the thickness of the load-bearing walls of the combustion chamber is locally increased to the extent to which a load-bearing cross-section is removed through the mixed air holes in the circumferential direction. According to the invention, it is possible to use this solution in single-layer as well as in double-layer combustion chamber walls. As far as double-layer combustion chamber walls are concerned, it is possible according to the invention to provide with a greater thickness or to thicken only one layer, for example the load-bearing external combustion chamber wall or the hot internal combustion chamber wall, or both.

Thus, the solution according to the invention has the advantage that the rigidity of the combustion chamber wall no longer varies in the longitudinal direction, but is instead constant in particular in the area of the mixed air holes, and in particular as compared to the areas in which no mixed air holes are formed. In this way, deformations through external loads are not concentrated in the area that is provided with the mixed air holes. Furthermore, a gap that can emerge between the shingle (internal combustion chamber wall) and the shingle support (external combustion chamber wall) becomes smaller thanks to the constant rigidity.

While in the constructions that are known from the state of the art the crack growth from one mixed air hole to another is a significant failure mechanism in the combustion chamber, the thickening or increase in thickness of the combustion chamber wall according to the invention provides for an increase in rigidity and strength of the combustion chamber wall especially in the areas that are weakened by the mixed air holes. In this manner it is possible to minimize crack formation and crack growth. This is done with a minimal material effort or a minimal increase in weight through the thickening of the combustion chamber wall.

The invention can be used in combustion chamber walls that are manufactured as cast parts as well as in combustion chamber walls that are made by means of a generative method (laser sintering, ALM, additive layer manufacturing). In combustion chambers that are made of sheet metal it is possible according to the invention to use specially contoured boards, or to manufacture the thinner areas of the walls by means of flow turning.

In an analogous manner, the invention can also be used with combustion chamber walls made of fiber-reinforced ceramic material (CMC). Here, the number of layers of the ceramic fiber fabrics or windings is locally increased in the area of the mixed air holes. This entails only a small additional effort, since the wall is principally composed of multiple layers. The number of layers is merely increased in the area of the mixed air holes, for example from 12 to 20. When it comes to CMC, the increase in wall thickness is greater, since the wall temperature can be higher, meaning that less cooling air has to be used, and thus more air is to be guided through the mixed air holes, by which their diameter is increased beyond what is possible in a metallic construction. The layers can be inserted on the internal or the external side or as additional intermediate layers with a limited axial extension.

In addition, when it comes to particular patterns of mixed air holes in a double-wall combustion chamber, it is advantageous if there is no more narrow web between the mixed air holes where the mixed air holes are in close proximity to one another, and if the two mixed air holes that are located in close proximity to one another in the shingle are instead supplied with air through a single opening in the cold combustion chamber wall. Through the elimination of the web the shingle can be thickened towards the exterior. This can also be done in the form of a rib on the cold side of the shingle, which then protrudes through the opening in the cold combustion chamber wall.

In any case, the increase in thickness of the combustion chamber wall is effected in such a manner that the mixed air holes do not reduce the rigidity of the combustion chamber wall.

In the following, the invention is described in connection to the drawing by referring to exemplary embodiments. Herein:

FIG. 1 shows a schematic rendering of a gas turbine engine according to the present invention,

FIG. 2 shows a longitudinal cross-section of a combustion chamber according to the state of the art,

FIG. 3 shows a schematic view of an arrangement of mixed air holes according to the state of the art,

FIG. 4 shows a view, analogous to FIG. 3, of an arrangement of mixed air holes according to the invention,

FIG. 5 shows a schematic side view of a combustion chamber, analogous to FIG. 2, of a first exemplary embodiment of the invention, and

FIG. 6 shows a view, analogous to FIG. 5, of another exemplary embodiment of the invention.

The gas turbine engine 110 according to FIG. 5 represents a general example of a turbomachine in which the invention can be used. The engine 110 is embodied in the conventional manner and comprises, arranged in succession in the flow direction, an air inlet 111, a fan 112 that is circulating inside a housing, a medium-pressure compressor 113, a high-pressure compressor 114, a combustion chamber 115, a high-pressure turbine 116, a medium-pressure turbine 117 and a low-pressure turbine 118, as well as an exhaust nozzle 119, which are all arranged around a central engine axis 101.

The medium-pressure compressor 113 and the high-pressure compressor 114 comprise multiple stages, respectively, with each of these stages having an array of fixedly attached stationary guide blades 120 extending in the circumferential direction, which are generally referred to as stator blades and which protrude radially inwards from the core engine housing 121 through the compressors 113, 114 into a ring-shaped flow channel. Further, the compressors have an array of compressor rotor blades 122 that protrude radially outwards from a rotatable drum or disc 125, [and] which are coupled to hubs 126 of the high-pressure turbine 116 or of the medium-pressure turbine 117.

The turbine sections 116, 117, 118 have similar stages, comprising an array of fixedly attached guide blades 123 which are protruding through the turbines 116, 117, 118 in a radially inward direction from the housing 121 into the ring-shaped flow channel, and a subsequent array of turbine blades 124 that are protruding externally from a rotatable hub 126. In operation, the compressor drum or compressor disc 125 and the blades 122 arranged thereon as well as the turbine rotor hub 126 and the turbine rotor blades 124 arranged thereon rotate around the engine axis 101.

FIG. 2 shows an enlarged longitudinal section view of a combustion chamber wall as it is known from the state of the art. Here, a combustion chamber 1 with a central axis 25 is shown, comprising a combustion chamber head 3, a base plate 8 and a heat shield 2. A burner seal is identified by the reference sign 4. The combustion chamber 1 has an external cold combustion chamber wall 7 to which an internal, hot combustion chamber wall 6 is attached. For the supply of mixed air, mixed air holes 5 are provided. With a view to clarity, impingement cooling holes and effusion holes have been omitted in the rendering.

The internal combustion chamber wall 6 is provided with bolts 13, which are embodied as threaded bolts and are screwed in by means of nuts 14. The mounting of the combustion chamber 1 is carried out by using combustion chamber flanges 12 and combustion chamber suspensions 11.

Combustion chamber walls that are known from the state of the art and are made of sheet metal usually have a constant thickness in the range of 0.9 to 1.6 mm, while the combustion chamber walls that are manufactured as cast parts have wall thicknesses of between 1.2 and 2.5 mm.

FIGS. 3 and 4 show the arrangement of mixed air holes in a schematic side view of a combustion chamber wall. For example, FIG. 3 shows the allocation of mixed air holes as they are known from the state of the art. It is to be understood that the modification of the wall thickness and thus the rigidity of the combustion chamber wall depends on the arrangement and the pattern of the mixed air holes. Here, it is in particular the axial distance and the circumferential distance of the mixed air holes that has to be taken into account. The respective cross-sections of the mixed air holes play a role, as well.

The greater thickness (W) of the combustion chamber (6, 7) is formed with a wall thickness, wherein the maximal wall thickness is calculated based on the following equation:

W _(max) =C· ^(√{square root over ((A−Sr)/A)}) ·W ₀

-   -   With     -   W_(max): maximal wall thickness     -   W₀: nominal wall thickness     -   A: distance between the hole centers of neighboring holes     -   Sr: sum of the hole radiuses of neighboring holes     -   C: power factor 0.7 . . . 1.3: to be selected by the design         engineer based on previous experience. This factor can take on         different values for different applications (depending on         experience).

Thus, i.e. for a power factor=1, the following instruction results:

If the remaining web thickness between neighboring mixed air holes falls below the sum of the cross-sections of the two mixed air holes by more than 20%, the wall thickness is increased by at least 27%.

If the remaining web thickness between neighboring mixed air holes falls below the mean value of the cross-sections of the two mixed air holes, the wall thickness is increased by substantially 41%.

If the remaining web thickness between neighboring mixed air holes falls below the mean value of the radiuses of the two mixed air holes, the wall thickness is increased by substantially 73%.

Here, it is irrelevant whether the smallest web thickness occurs between the mixed air holes of a row or between the mixed air holes of neighboring rows. This determines only the axial position of the maximal wall thickness. If the smallest web thickness lies between the mixed air holes of a row, the maximum of the wall thickness lies at the axial position of the axes of the mixed air hole row. If the minimal web thickness lies between the mixed air holes of neighboring mixed air hole rows, the maximal wall thickness lies between the central axes of the two rows of the mixed air holes substantially in the middle between the rows.

The axial extension of the thickening for a mixed air hole row is substantially limited to the area between an upstream hole diameter and a downstream hole diameter.

The axial extension of the thickening for two mixed air hole rows is substantially limited to the area between a hole diameter of the upstream mixed air hole row in the upstream direction and a hole diameter of the downstream mixed air hole row in the downstream direction.

If different mixed air hole diameters are present in one row, the largest diameter of the respective hole row applies with respect to these limitations.

In order to simplify the manufacturing process, the enlargement of the wall thickness can be realized in a ramp in front of the ligament that determines the thickness, followed by an area of constantly high wall thickness in the area of the mixed air holes and a ramp back to a smaller wall thickness, which is then substantially maintained up until shortly before the end of the combustion chamber. Here, the substantially constant wall thickness in front of the mixed air hole row does not have to be identical to the substantially constant wall thickness downstream of the same. In this manner, the transitions in wall thickness are designed so as to be fluid in order to avoid voltage peaks through cross-sectional jumps.

According to the invention, it is for example possible to increase the sheet metal thickness of the external cold combustion chamber wall 7 from 1.2 mm to 1.6 mm, while the thickness of an internal hot combustion chamber wall 6 that is embodied as a cast part is increased in the area of the mixed air holes from 1.4 mm to 2 mm. Thus it is possible in known patterns or arrangements of mixed air holes 5 to achieve a modification of the rigidity through an increase of the wall thickness, namely in such a manner that any weakening of the walls which occurs without the thickening is compensated for.

FIG. 4 illustrates an embodiment that is possible according to the invention in which the two mixed air hole rows are considerably approximated in the circumferential direction or almost overlap. Without an increase in wall thickness, as it is provided according to the invention, the weakening of the combustion chamber wall would be further increased. Thus, according to the invention, a stronger thickening is effected in this area, as will be described in the following in connection to FIGS. 5 and 6. For example, a sheet metal thickness of a combustion chamber wall can be increased from 1.2 mm to 1.8 mm. According to the invention, the wall thickness of a cast part of 1.4 mm can for example be increased to 2.5 mm in the area where the mixed air holes overlap.

As has been mentioned, the invention can be used in single-wall as well as in double-wall combustion chambers. In a combustion chamber with a single-wall, the wall thickness of the sheet metal is for example increased in the area of the mixed air holes, or the cross-section of the adjoining area which is not provided with mixed air holes is reduced by means of flow turning. Through the flow turning, standardized sheet metal thicknesses are abandoned to arrive at a wall thickness that is adjusted to the local requirements. Structural components with locally adjusted wall thickness that are produced by means of flow turning can be manufactured in a more cost-effective manner as compared to structural components that are mated from multiple sheet metals, forged or cast parts. If a combustion chamber wall has a multi-layer wall construction, which is for example manufactured as a cartridge or by mating laminated sheet metals, it is possible according to the invention to adjust the wall thickness in the area of the mixed air holes analogously to the local requirements.

FIG. 5 shows a sectional view of a combustion chamber wall that is analogous to FIG. 2. In FIG. 2, the wall thickness across the length of the combustion chamber wall is represented in the form of a diagram in the top part of the image. As can be seen from it, the combustion chamber wall has a constant wall thickness W across its entire length. In contrast to that, a thickening of the wall in the area of the mixed air holes 5 and thus a greater wall thickness is provided in the exemplary embodiment shown in FIG. 5, as can be seen in the diagram in the top half of the image of FIG. 5.

FIG. 5 shows a sectional view of a construction in which the external cold combustion chamber wall 7 as well as the internal hot combustion chamber wall 8 are configured in a thickened manner. In this way, the reduction of the cross-section of the two combustion chamber walls 7, 8 that is available in terms of strength is compensated for by the thickening.

FIG. 6 shows another exemplary embodiment in a rendering that is analogous to FIG. 5. As can be seen here, a further increase in wall thickness occurs in addition to the thickening or increase in wall thickness in the area between the mixed air holes 5 or in the area of their overlapping (see also FIG. 4) as it is provided in FIG. 5. This can particularly also be seen in the diagram in the top half of the rendering in FIG. 6.

PARTS LIST

1 combustion chamber

2 heat shield

3 combustion chamber head

4 burner seal

5 mixed air

6 internal, hot combustion chamber wall/segment/shingle

7 internal, cold combustion chamber wall

8 base plate

9 central axis

10 sealing lip

11 combustion chamber suspension

12 combustion chamber flange

13 bolt

14 nut

101 engine central axis

110 gas turbine engine/core engine

111 air inlet

112 fan

113 medium-pressure compressor (compactor)

114 high-pressure compressor

115 combustion chamber

116 high-pressure turbine

117 medium-pressure turbine

118 low-pressure turbine

119 exhaust nozzle

120 guide blades

121 engine cowling

122 compressor rotor blades

123 guide blades

124 turbine blades

125 compressor drum or compressor disc

126 turbine rotor hub

127 outlet cone

W wall thickness 

1. Gas turbine combustion chamber, comprising at least one combustion chamber wall in which mixed air holes are formed in a predefined area that extends around the combustion chamber in a ring-shaped manner with respect to the central axis of the combustion chamber in a central area of the same, wherein the combustion chamber wall has a greater thickness in the ring-shaped area of the mixed air holes than in the areas that are not provided with mixed air holes.
 2. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall has a substantially constant rigidity in all areas, in particular in the longitudinal direction with respect to the throughflow direction of the combustion chamber.
 3. Gas turbine combustion chamber according to claim 1, wherein the greater thickness of the combustion chamber is formed with a wall thickness, wherein the maximal wall thickness is calculated based on the following equation: W _(max) =C· ^(√{square root over ((A−Sr)/A)}) ·W ₀ W_(max): maximal wall thickness W₀: nominal wall thickness A: distance between the hole centers of neighboring holes Sr: sum of the hole radiuses of neighboring holes C: power factor 0.7 . . . 1.3:
 4. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is embodied with a single layer.
 5. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is embodied with a double layer, and in that at least one of the combustion chamber walls is provided with a greater wall thickness in the area of the mixed air holes.
 6. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is manufactured as a cast part.
 7. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is manufactured by means of a generative method.
 8. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is manufactured from contoured sheet metal materials.
 9. Gas turbine combustion chamber according to claim 1, wherein the combustion chamber wall is manufactured from a fiber-reinforced ceramic material. 